Surgical instrumentation and method for forming a passage in bone having an enlarged cross-sectional portion

ABSTRACT

A surgical instrument and method for forming a passage in bone having an enlarged cross-sectional portion is provided. The instrument includes an elongate member and a cutting element engaged thereto and transitionable between a retracted configuration for extending through a first portion of the passage and an expanded configuration for forming a second portion of the passage having an enlarged cross-section. In one embodiment, the cutting element is transitioned between the retracted and expanded configurations by axially displacing the cutting element relative to the elongate member. In another embodiment, the elongate member includes a tapping thread configured to cut threads along the first portion of the passage, and the cutting element is a blade configured to form the enlarged cross-section when transitioned to the expanded configuration. In another embodiment, the cutting element is arranged in an axial orientation when in the retracted configuration and an angular orientation when in the expanded configuration.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of Provisional ApplicationSer. No. 60/298,985, filed on Jun. 18, 2001 and entitled VariableDiameter Passage Tap Apparatus, the contents of which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to the field of surgicalinstrumentation and methods, and more specifically relates to surgicalinstrumentation and methods for forming a passage in bone having anenlarged cross-sectional portion, and more particularly within avertebral body.

BACKGROUND OF THE INVENTION

Skeletal members are formed of bone tissue and other structures such ascartilage. For various reasons, skeletal members sometimes fracture,weaken or deteriorate over time. In other instances, skeletal membersmay be deformed or diseased. In either case, treatment of the skeletalmember usually requires some type of artificial support or stabilizationto promote healing and/or correction of abnormalities.

With specific regard to treatment of the spine, plates or rods aretypically attached to the portion of the spinal column being treated toprovide the requisite amount of support and/or stabilization. In manycases, attachment of the plates or rods to the spine is accomplished byengaging a number of bone anchors, such as bone screws, to one or morevertebral bodies. In such applications, the bone screws are sometimesengaged to the vertebral bodies via extension through the pedicle whichis mostly comprised of cancellous or porous bone tissue. When dealingwith patients having soft bone tissue or with patients afflicted with abone weakening disease (e.g., osteoporosis), conventional bone screwshave a tendency to cut out or loosen as a result of insufficient bonestrength.

To compensate for soft or weakened bone tissue, bone cement or anothertype of material is sometimes introduced adjacent the threaded portionof the bone screw to strengthen the bone. The bone cement provides amore secure anchoring arrangement to prevent the screw from cutting outor loosening. The cement material is typically introduced into the bonevia passage through an axial opening extending along a length of thescrew and exiting through a series of fenestration openings incommunication with the axial opening and positioned at intermittentlocation along the length of the screw. Preferably, the bone cementshould be distributed uniformly about the threaded portion of the bonescrew with minimal disruption to the adjacent bone tissue.

In a prior method for treating the spine using bone screws, a uniformpassage having a diameter equal to or slightly less than the screwdiameter is formed through the pedicle region of the vertebral body. Abone screw is then threaded into the passage to a predeterminedinsertion depth, with the threads of the bone screw engaged tightlyagainst adjacent bone tissue. Once the bone screw is properly positionedwithin the vertebral body, bone cement is injected through the axialopening in the bone screw and introduced into the bone by way of anumber of the fenestration openings. Notably, this method of screwinsertion and anchoring typically results in an uneven distribution ofbone cement around the threaded portion of the bone screw. Additionally,rapid injection of the bone cement can lead to fluid pressure buildup,sometimes resulting in disruption of the cancellous bone tissue in thearea adjacent the fenestration openings.

In another prior method for treating the spine using bone screws, auniform passage having a diameter somewhat larger than the screwdiameter is formed through the pedicle region of the vertebral body. Ina specific application, the diameter of the passage is about 1.5 to 2.0millimeters larger than the diameter of the bone screw. The bone screwis then inserted into the passage, and once properly positioned withinthe vertebral body, bone cement is introduced into the passage to fillup the void or spacing between the screw and the walls of the passage.However, this method of screw insertion and anchoring requires theformation of an oversized screw insertion passage extending through thepedicle. Notably, the formation of an oversized passage results in theremoval of a relatively large amount of vertebral bone tissue, therebytending to compromise the structural integrity of the pedicle.

Thus, there is a general need in the industry to provide improvedsurgical instrumentation and methods for forming a passage in bonehaving an enlarged cross-sectional portion than is currently availablewithin the industry. The present invention meets this need and providesother benefits and advantages in a novel and unobvious manner.

SUMMARY OF THE INVENTION

The present invention relates generally to surgical instrumentation andmethods for forming a passage in bone having an enlarged cross-sectionalportion. While the actual nature of the invention covered herein canonly be determined with reference to the claims appended hereto, certainforms of the invention that are characteristic of the preferredembodiments disclosed herein are described briefly as follows.

In one form of the present invention, a surgical instrument is providedwhich includes an elongate member and at least one cutting elementengaged thereto. The cutting element is transitionable between aretracted configuration capable of extending through a first portion ofa passage in bone and an expanded configuration capable of forming asecond portion of the passage having an enlarged cross-section, withaxial displacement of the cutting element relative to the elongatemember causing the cutting element to transition between the retractedand expanded configurations.

In another form of the present invention, a surgical instrument isprovided which includes an elongate member, a first cutting elementdisposed along the elongate member for forming a first portion of apassage in bone, and a second cutting element disposed along theelongate member and being transitionable between a retractedconfiguration for extending through the first portion of the passage andan expanded configuration for forming a second portion of the passagehaving an enlarged cross-sectional portion.

In another form of the present invention, a surgical instrument isprovided which includes an elongate member, a tapping thread definedalong at least a portion of the elongate member configured to form athreaded portion of a passage in bone, and a cutting element engagedwith the elongate member and being transitionable between a retractedconfiguration for extending through the threaded portion of the passageand an expanded configuration for forming an enlarged cross-sectionalportion of the passage.

In another form of the present invention, a surgical instrument isprovided which includes means for tapping threads along a portion of apassage in bone, means for forming an enlarged cross-sectional portionof the passage, and means for transitioning the means for formingbetween a retracted configuration for extending through the threadedportion of the passage and an expanded configuration for forming theenlarged cross-sectional portion of the passage.

In another form of the present invention, a surgical instrument isprovided which includes an elongate member extending along an axis andincluding an expandable portion having at least one cutting element thatis transitionable between an axial orientation for forming an axialpassage in bone and an angular orientation for enlarging a portion ofthe axial passage.

In another form of the present invention, a surgical instrument isprovided which includes an elongate member and at least one cuttingelement engaged with the elongate member and being transitionablebetween a retracted configuration for extending through a passage inbone and an expanded configuration for enlarging a portion of thepassage, with the cutting element being outwardly biased toward theexpanded configuration. The instrument also includes a retention elementinteracting with the cutting element to selectively maintain the cuttingelement in the retracted configuration.

In another form of the present invention, a surgical method is providedwhich includes the steps of providing a surgical instrument having anelongate member and at least one cutting element engaged with theelongate member and being transitionable between a retractedconfiguration and an expanded configuration, forming a passage in bone,displacing the cutting element along the passage while in the retractedconfiguration, transitioning the cutting element to the expandedconfiguration and enlarging a portion of the passage, transitioning thecutting element to the retracted configuration and removing the surgicalinstrument from the passage.

It is one object of the present invention to provide improved surgicalinstrumentation and methods for forming a passage in bone tissue havingan enlarged cross-section portion.

Further objects, features, advantages, benefits, and aspects of thepresent invention will become apparent from the drawings and descriptioncontained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional side view of a skeletal memberillustrating a surgical instrument according to one form of the presentinvention, as shown in a closed-tip configuration.

FIG. 2 is the surgical instrument illustrated in FIG. 1, as shown in anopen-tip configuration.

FIG. 3 is a partial cross-sectional side view of a skeletal memberillustrating a surgical instrument according to another embodiment ofthe present invention, as shown in a closed-tip configuration.

FIG. 4 is a partial cross-sectional side view of a skeletal memberillustrating a surgical instrument according to another embodiment ofthe present invention, as shown in a closed-tip configuration.

FIG. 5 is a perspective view of a surgical instrument according toanother form of the present invention.

FIG. 6 is a side view of the distal end portion of the surgicalinstrument illustrated in FIG. 5, as shown in a retracted configuration.

FIG. 7 is a side view of the distal end portion of the surgicalinstrument illustrated in FIG. 5, as shown in an expanded configuration.

FIG. 8 is a perspective view of the distal end portion of the surgicalinstrument illustrate d in FIG. 6, as shown in the retractedconfiguration.

FIG. 9 is a perspective view of the distal end portion of the surgicalinstrument illustrated in FIG. 7, as shown in the expandedconfiguration.

FIG. 10 is a cross-sectional view of the distal end portion of thesurgical instrument illustrated in FIG. 6, as shown in the retractedconfiguration.

FIG. 11 is a cross-sectional view of the distal end portion of thesurgical instrument illustrated in FIG. 7, as shown in the expandedconfiguration.

FIG. 12 is a perspective view of one embodiment of an actuator mechanismfor use with the surgical instrument illustrated in FIG. 5.

FIG. 13 is a cross-sectional view of the actuator mechanism illustratedin FIG. 12.

FIG. 14 is a perspective view of the distal end portion of a surgicalinstrument according to another form of the present invention, as shownin an expanded configuration.

FIG. 15 is a partial cross-sectional side view of a skeletal member,depicting the formation of a threaded portion of an axial passage by thesurgical instrument illustrated in FIG. 5.

FIG. 16 is a partial cross-sectional side view of the skeletal memberillustrated in FIG. 15, depicting the formation of an enlargedcross-sectional of the axial passage by the surgical instrumentillustrated in FIG. 5.

FIG. 17 is a side view of a fenestrated bone screw for use inassociation with the present invention.

FIG. 18 is a cross-sectional view of the fenestrated bone screwillustrated in FIG. 17.

FIG. 19 is a partial cross-sectional side view of the skeletal memberillustrated in FIG. 16, depicting insertion of the fenestrated bonescrew into the axial passage with the fenestration openings positionedadjacent the enlarged portion of the axial passage.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation on the scope of theinvention is hereby intended, and that alterations and furthermodifications in the illustrated devices and further applications of theprinciples of the invention as illustrated herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

Referring to FIGS. 1 and 2, shown therein is a surgical instrument 20according to one form of the present invention. As will be discussed indetail below, the instrument 20 and other embodiments of the presentinvention are used to form a passage in a skeletal member having anenlarged cross-sectional portion. In one embodiment of the invention,the surgical instruments and methods illustrated and described hereinare used in association with treatment of the spine. It should beunderstood, however, that the present invention may also be used inassociation with applications outside of the spinal field. It shouldalso be understood that although the present invention is illustratedand described in the context of treatment of a human spine, thetreatment of other animals is also contemplated. Moreover, although thepresent invention is illustrated and described as being used inassociation with intrabody applications to form a passage in a vertebralbody for receiving a bone anchor, it should be understood that otherapplications are also contemplated. For example, the present inventioncould also be used in association with interbody applications to form apassage between adjacent vertebral bodies, with the passage having anenlarged cross-sectional portion sized to receive a spinal implant suchas a threaded or unthreaded fusion cage.

The surgical instrument 20 is generally comprised of an elongate member22 and an actuator mechanism 24. The elongate member 22 extendsgenerally along a longitudinal axis L and has a proximal end portion 22a and a distal end portion 22 b. The actuator mechanism 24 includes anactuator handle 25 disposed adjacent the proximal end portion 22 a ofthe elongate member 22. Although the illustrated embodiment depicts theelongate member 22 as having a generally linear configuration, it shouldbe understood that other configurations are also contemplated, such as,for example, a curvilinear configuration or an angled configuration.

The elongate member 22 is generally comprised of a hollow shaft orsleeve 26 and an expandable tip 28 extending from the distal end portionof the sleeve 26. The expandable tip 28 includes a pair of cuttingelements 30, 32 that are transitionable between a retracted or closedconfiguration (FIG. 1) for forming an axial passage in the vertebralbody V, and an expanded or open configuration (FIG. 2) for forming anenlarged cross-sectional portion of the axial passage. When in theretracted configuration, the cutting elements 30, 32 are preferablyaligned generally along longitudinal axis L and preferably have an outercross-section equal to or less than the outer cross-section of thesleeve 26. When in the expanded configuration, the cutting elements 30,32 are preferably angled relative to longitudinal axis L at an acuteangle θ and define an enlarged outer cross-section relative to theretracted configuration. In one embodiment of the invention, when in theangular orientation, the cutting elements 30, 32 are angled at an angleθ of about 45 degrees. However, it should be understood that otherangles are also contemplated as falling within the scope of the presentinvention, including any angle θ falling between 0 degrees and 180degrees. As will be discussed in greater detail below, the expandabletip 28 is configured to transition between the axial and angularorientations in response to a mechanically induced force. Such force maybe effected, for example, via the selective actuation of the actuatormechanism 24.

Although the expandable tip 28 has been illustrated and described asincluding a pair of cutting elements 30, 32 disposed generally oppositeone another, it should be understood that the tip 28 could be comprisedof any number of cutting elements, including a single cutting element orthree or more cutting elements. Additionally, although the cuttingelements 30, 32 have been illustrated and described as being positionedadjacent the distal end 22 b of the elongate member 22, it should beunderstood that the cutting elements 30, 32 may be disposed at otheraxial locations as well. It should also be understood that a series ofcutting elements may be disposed at multiple axial locations along theelongate member 22.

The cutting elements 30, 32 preferably have distal ends 34 that arepointed to facilitate penetration into bone tissue to form an axialpassage in the vertebral body V when the cutting elements 30, 32 aredisposed in the axial orientation. However, it should be understood thatother configurations of the distal ends 34 are also contemplated. Forexample, the distal ends 34 could alternatively have a bluntconfiguration, such as a rounded or flat shape, or could have any othersuitable shape or configuration as would occur to one of skill in theart. The cutting elements 30, 32 also preferably include at least onecutting edge 36 to facilitate formation of the axial passage whendisposed in the axial orientation, and to facilitate formation of anenlarged cross-sectional portion after the cutting elements 30, 32 aretransitioned to the angular orientation. In one embodiment of theinvention, the cutting edge 36 is defined by a cutting blade extendinggenerally along the longitudinal axis L. In another embodiment of theinvention, the cutting edge 36 is defined by a flute, such as, forexample, an axial or helical drill flute. In yet another embodiment ofthe invention, the cutting edge 36 is defined by a tapping threadconfigured to form threads along the inner wall of the axial passage. Instill another embodiment of the invention, a cutting edge may be formedalong a portion of the sleeve 26 to facilitate formation of the axialpassage in the vertebral body V.

Although one specific embodiment of the cutting elements 30, 32 has beenillustrated and described herein, it should be understood that othershapes and configurations of cutting elements are also contemplated.Indeed, any cutting element that is suitable for cutting bone tissue toform a passage having an enlarged cross-sectional portion iscontemplated as falling within the scope of the present invention. Forexample, as shown in FIG. 3, the expandable tip 48 includes a pair ofopposing cutting elements 50, 52. The distal end portions of the cuttingelements 50, 52 are inwardly tapered so as to define a streamlined,wedge-shape or conical configuration when the cutting elements 50, 52are disposed in an axial orientation. Notably, the cutting elements 50,52 define a single pointed tip 54 when disposed in the axialorientation, thereby tending to further aid in the formation of theaxial passage in the vertebral body V. Similar to cutting elements 30,32, the cutting elements 50, 52 preferably include at least one cuttingedge 56 to facilitate formation of the axial passage and the enlargedcross-sectional portion of the passage after the cutting elements 50, 52are transitioned to an angular orientation. Aside from the shape andconfiguration of the cutting elements 50, 52, the expandable tip 48functions in a manner similar to that of the expandable tip 28.

In a preferred embodiment of the invention, the cutting elements 30, 32are biased or urged away from one another toward the angular orientationillustrated in FIG. 2. The biasing force may be generated by one or morebiasing mechanisms (not shown), such as, for example, a spring orspring-like device. The cutting elements 30, 32 are preferablyselectively maintained in the axial orientation illustrated in FIG. 1 bya retention mechanism. In one embodiment of the invention, the sleeve 26functions as the retention mechanism. As illustrated in FIG. 1, at leasta portion of each cutting element 30, 32 is initially disposed withinthe sleeve 26 to prevent the cutting elements 30, 32 from opening orexpanding toward the angular orientation. However, as illustrated inFIG. 2, when the expandable tip 28 is axially displaced relative to thesleeve 26 such that the cutting elements 30, 32 are displaced beyond thedistal end of sleeve 26, the cutting elements 30, 32 are transitioned orexpanded toward the angular orientation.

In one embodiment of the invention, the actuator mechanism 24 isgenerally comprised of an actuator handle 25 and a drive shaft 40. Theactuator handle 25 includes a pair of arms 42, 44 extending laterallyfrom a proximal end portion of the drive shaft 40 in generally oppositedirections. The drive shaft 40 is preferably slidably and rotatablydisposed within the sleeve 26, with the cutting elements 30, 32 beingoperatively coupled to the distal end portion of shaft 40. In oneembodiment of the invention, the cutting elements 30, 32 are pivotallycoupled to the distal end portion of shaft 40. However, it should beunderstood that other suitable means for coupling the cutting elements30, 32 to the distal end portion of shaft 40 are also contemplated asfalling within the scope of the present invention.

The arms 42, 44 of the actuator handle 25 preferably extendperpendicularly from the drive shaft 40 to form a T-handle arrangement.However, other shapes and configurations of actuator handle 25 are alsocontemplated. For example, as shown in FIG. 3, instead of beingconnected to drive shaft 40, the arms 42, 44 of actuator handle 25 mayalternatively be connected to and extend laterally from the sleeve 26.As also shown in the embodiment of FIG. 3, an actuator knob 58 may beoperatively attached to the proximal end portion of the drive shaft 40.In another embodiment of the invention illustrated in FIG. 4, theT-shaped actuator handle 25 may be replaced by an actuator handle 60extending generally along longitudinal axis L. The actuator handle 60 isoperatively attached to the proximal end portion of the drive shaft 40and includes a cylindrical-shaped gripping portion 62 defining acontoured gripping surface 64. Aside from its shape and configuration,the actuator handle 60 functions in a manner similar to that of actuatorhandle 25.

The actuator handle 25, 60 preferably defines an axially facing bearingor tapping surface 46 configured to provide a means for applying anaxial force to the drive shaft 40 and/or the sleeve 26 to facilitateformation of the axial passage within the vertebral body V. The bearingsurface 46 may be defined by the arms 42, 44, the cylindrical grippingportion 62, the proximal end of sleeve 26, and/or the actuator knob 58.Preferably, the bearing surface 46 is generally flat such that an axialforce might be applied directly by the user's hand and/or by way of adriving tool, such as, for example, a mallet or another type of impacttool.

Application of an axial force to the bearing surface 46 correspondinglytransmits an axial force to the drive shaft 40, and more specifically tothe cutting elements 30, 32. As should be apparent, application of anaxial force to the actuator handle 24, 60 when the cutting elements 30,32 are in an axial orientation will cause the cutting elements 30, 32 topenetrate and cut into bone tissue to form an axial passage in thevertebral body V. Although the distal ends 34 of the cutting elements30, 32 are illustrated and described as extending beyond the distal endof the sleeve 26 when in the axial orientation, it should be understoodthat the distal ends 34 could alternatively be disposed entirely withthe sleeve 26 when disposed in the axial orientation. In such anembodiment, the sleeve 26 may be configured to form the axial passagewithin the vertebral body V. For example, the distal end of sleeve 26could be configured to include a cutting edge to facilitate penetrationand cutting into bone tissue. Alternatively, an axial passage could bepreformed into the vertebral body V via a separate instrument, such as,for example, a conventional drill or reamer, with the instrument 20being used to form an enlarged portion of the pre-formed passage.

Following formation of the axial passage in the vertebral body V, theexpandable tip 28 is transitioned from the axial orientation illustratedin FIG. 1 toward the angular orientation illustrated in FIG. 2. Asdiscussed above, such transitioning may occur in response to theapplication of a mechanically induced force, such as might be effected,for example, by displacing the actuator handle 25 relative to the sleeve26. In one embodiment of the invention, axial displacement of the driveshaft 40 relative to the sleeve 26 correspondingly causes the cuttingelements 30, 32 to transition between the axial and angularorientations. Such axial displacement may be effected by applying anaxial force to the actuator handle 25 while maintaining the sleeve 26 ina stationary position, or by pulling the sleeve 26 toward the arms 40,42 of actuator handle 25 while maintaining the handle 25 in a stationaryposition, or by a combination of these operations. In an alternativeembodiment of the invention, the surgical instrument 20 could beconfigured such that rotational displacement of the sleeve 26 relativeto the drive shaft 40 would correspondingly cause relative axialdisplacement between the sleeve 26 and the expandable tip 28. Such anoperation might be accomplished, for example, by providing the driveshaft 40 with external threads which engage internal threads definedalong the interior of sleeve 26. As should be apparent, rotating thehandle 25 about the longitudinal axis L would correspondingly axiallydisplace the drive shaft 40 and the expandable tip 28 relative to thesleeve 26 to transition the cutting elements 30, 32 between the axialand angular orientation.

Once the expandable tip 28 is transitioned to the angular orientationillustrated in FIG. 2, a rotational force (i.e., torque) is applied tothe actuator handle 25. Rotating the actuator handle 25 in turn rotatesthe cutting elements 30, 32 generally about the longitudinal axis L tofacilitate enlargement of a cross-sectional portion of the axial passagein the vertebral body V. The rotational force or torque may be applieddirectly by the user's hand via the arms 42, 44 of handle 25, or by adriving tool such as a wrench or drive motor. The rotational force ortorque exerted onto the handle 25 is in turn transmitted to the cuttingelements 30, 32, either directly via the drive shaft 40 or indirectlyvia the sleeve 26. As should be apparent, rotating the cutting elements30, 32 about the longitudinal axis L when the cutting elements 30, 32are in the angular orientation illustrated in FIG. 2 will cause thecutting edges 36 to cut into the bone tissue to enlarge the distal endportion of the axial passage in the vertebral body V.

Having described the various structural features of the surgicalinstrument 20, a method of using the surgical instrument 20 will now bediscussed in accordance with one form of the present invention.Referring once again to FIG. 1, when the expandable tip 28 is disposedin the axial or retracted orientation, the cutting elements 30, 32 aregenerally aligned with the longitudinal axis L and define an outerdiameter d₁ that is preferably equal to or slightly less than the outerdiameter of the sleeve 26. An axial force is applied to the actuatorhandle 25 in the direction of arrow A, which in turn causes the cuttingelements 30, 32 to penetrate and cut into bone tissue to form an axialpassage through the pedicle P and into the vertebral body V. The axialpassage preferably has an inner diameter substantially equal to theouter diameter d₁ of the expandable tip 28. As described above, suchaxial force may be applied to the axially facing surface 46, eitherdirectly by the user's hand or by way of an impact tool. In anotherembodiment of the invention, a rotational force may be applied to thehandle 25 to rotate the cutting elements 30, 32 about the longitudinalaxis L to cause the cutting edges 36 and the distal tips 34 to cut intobone tissue to form the axial passage in the vertebral body V. In yetanother embodiment, both an axial and rotational force may be applied tothe handle 25 to form the axial passage in the vertebral body V.

Although the axial passage extending through the pedicle P and thevertebral body V has been illustrated and described as having agenerally circular cross-section, other cross sections are alsocontemplated as falling within the scope of the present invention. Forexample, the axial passage may have an elliptical, rectangular, orpolygonal cross-section, or any other suitable cross-section that wouldbe apparent to one of skill in the art. Moreover, although the surgicalinstrument 20 has been illustrated and described as being used to formthe axial passage, it should be understood that an axial passage havinga diameter d₁ may be preformed in the vertebral body V. In such case,the expandable tip 28 may be displaced along the preformed axial passage(while in the axial orientation) until disposed in the positionillustrated in FIG. 1.

Following formation of the axial passage, the cutting elements 30, 32are transitioned toward the angular or expanded orientation illustratedin FIG. 2 to form an enlarged cross-sectional portion of the passage. Asdiscussed above, such transitioning may be accomplished by displacingthe expandable tip 28 relative to the sleeve 26, either by displacingthe handle 25 and drive shaft 40 in the direction of arrow A and/or bydisplacing the sleeve 26 in the direction of arrow B. When transitionedto the angular orientation, the cutting elements 30, 32 are eachdisposed at an angle θ relative to the longitudinal axis L to define anenlarged/expanded outer cross-section.

After being transitioned to the angular orientation, the cuttingelements 30, 32 are rotated about the longitudinal axis L which causesthe cutting edges 36 and the distal tips 34 to cut into vertebral bonetissue to form an enlarged cross-sectional portion of the axial passagehaving a diameter d₂. In an alternative embodiment of the invention, anaxial force may be applied to handle 25 in the direction of arrow A tocause the cutting elements 30, 32 to penetrate and cut into vertebralbone tissue to form the enlarged cross-sectional portion of the axialpassage. In another embodiment, both a rotational force and an axialforce may be applied to the handle 25 to form the enlargedcross-sectional portion of the axial passage. It should be understoodthat the cutting elements 30, 32 need not necessarily be instantaneouslytransitioned to the angular orientation illustrated in FIG. 2, but maybe gradually transitioned toward the angular orientation duringformation of the enlarged cross-sectional portion of the axial passage.Furthermore, although the enlarged portion of the axial passage has beenillustrated and described as having a generally circular cross-section,as discussed above, other cross-sections are also contemplated asfalling within the scope of the present invention.

Following formation of the enlarged cross-sectional portion of the axialpassage, the cutting elements 30, 32 are transitioned back to the axialorientation illustrated in FIG. 1 and the expandable tip 28 and theremainder of the instrument 20 are removed from the vertebral body V. Abone anchor (not shown) may then be inserted into the axial passage,preferably having an outer diameter closely corresponding to the innerdiameter d₁ of the axial passage. The enlarged portion of the axialpassage is then filled with an anchoring material, such as bone cementor other known anchoring material, to secure the bone anchor inposition. In one embodiment of the invention, the bone anchor may beconfigured as a fenestrated bone screw defining an axial openingextending at least partially therethrough and a series of fenestrationopenings disposed in communication with the axial opening. Oneembodiment of a fenestrated bone screw suitable for use in associationwith the present invention is described in U.S. patent application Ser.No. 09/746,668 to Chappuis, filed on Dec. 20, 2000, the contents ofwhich are hereby incorporated by reference. It should be understood,however, that other suitable bone anchors are also contemplated for usewith the present invention, including both threaded and unthreaded boneanchor devices.

The bone screw is preferably positioned within the vertebral body V withthe fenestration openings disposed adjacent the enlarged cross-sectionalportion of the axial passage. As a result, bone cement may be injectedthrough the axial opening in the bone screw, out the fenestrationopenings, and into the enlarged cross-sectional portion of the axialpassage. As should be appreciated, the enlarged cross-sectional portionof the axial passage facilitates uniform distribution of the bone cementaround the threaded portion of the bone screw while minimizingdisruption to the cancellous bone tissue surrounding the bone screw.

Once the bone cement cures or hardens, a cement mantle is formed about aportion of the bone screw to more firmly secure the bone screw withinthe vertebral body V. As should be appreciated, the cement mantleeliminates or at least minimizes the likelihood of the bone screw fromloosening or cutting away from the vertebral body V. As should also beappreciated, enlargement of only a portion of the axial passage to theenlarged diameter d₂, while maintaining the remainder of the axialpassage at the diameter d₁, reduces the amount of bone material removedfrom the vertebral body V. As a result, disruption of the structuralintegrity of the vertebral body V, and particularly the pedicle P, islikewise minimized. In this manner, formation of the axial passage inthe vertebral body V and securing the bone screw within the axialpassage by way of a cement mantle is accomplished in a minimallyinvasive manner.

Referring now to FIG. 5, shown therein is a surgical instrument 100according to another form of the present invention. The surgicalinstrument 100 is generally comprised of an elongate member 102, acutting element 104 (FIG. 7), and an actuator mechanism 106. As willbecome apparent below, the elongate member 102 is preferably configuredto form threads along a portion of an axial passage in a skeletalmember. As will also become apparent, the cutting element 104 istransitionable between a retracted configuration and an expandedconfiguration via the selective actuation of actuator mechanism 106. Theretracted configuration permits extension of the cutting element 104through the threaded passage, while the expanded configuration isconfigured to form an enlarged cross-sectional portion of the axialpassage.

The elongate member 102 extends generally along a longitudinal axis Land has a proximal end portion 102 a and a distal end portion 102 b.Although the elongate member 102 is illustrated as having a generallylinear configuration, it should be understood that other configurationsare also contemplated, such as, for example, a curvilinear configurationor an angled configuration. Additionally, although the elongate member102 is illustrated as having a generally circular and substantiallyuniform outer cross-section, it should be understood that other shapesand configurations are also contemplated as would occur to one of skillin the art. In one embodiment of the invention, a handle 110 isoperatively attached to the proximal end portion 102 a of elongatemember 102. The handle 110 includes a cylindrical-shaped grippingportion 112 defining a gripping surface 114 to aid in the manipulationand positioning of surgical instrument 100 by the surgeon. Although aspecific embodiment of the handle 110 has been illustrated anddescribed, it should be understood other types and configurations ofhandles are also contemplated, such as, for example, a T-handlearrangement or any other suitable handle configuration that would occurto one of skill in the art. It should also be understood that thesurgical instrument 100 need not necessarily include a handle, but couldalternatively be configured to engage various types of driving tools orpossibly a drive motor.

In a preferred embodiment of the invention, a tapping thread 120 isdefined along the distal end portion 102 b of elongate member 102. Thetapping thread 120 is configured to form a threaded axial passage inbone tissue. As should be appreciated, the specific configuration of thetapping thread 120 will be determined by the type of threaded device tobe engaged within the threaded axial passage. As will be discussed infurther detail below, one such threaded device suitable for use inassociation with the present invention is a bone screw. However, othertypes of threaded devices are also contemplated, such as, for example,spinal implants including fusion cages.

In the illustrated embodiment of the invention, the tapping thread 120is configured to cut threads along a preformed passage in bone tissue.However, in an alternative embodiment of the invention, the distal endportion 102 b of elongate member 102 may be configured to form the axialpassage. For example, a self-drilling feature could be incorporated intothe design of the distal end portion 102 b, such as, for example, byincluding a cutting flute extending along the distal end portion 102 band/or by including a cutting edge or tip at the distal-most end of endportion 102 b. In another embodiment of the invention, the tappingthread 120 could be eliminated and replaced with another type of cuttingelement suitable for forming an axial passage in bone tissue. Forexample, referring to FIG. 14, shown therein is a surgical instrument300 according to another form of the invention. The surgical instrument300 is configured similar to surgical instrument 100 except for the factthat the distal end portion 302 is shaped like a drill. Specifically,the distal end portion 302 includes a cutting tip 304 and at least onecutting flute 306. The cutting flute 306 may be configured as an axialflute, a helical flute, or any other type of flute that would occur toone of skill in the art.

Referring now to FIGS. 6-11, shown therein is a retracted configuration(FIGS. 6, 8 and 10) and an expanded configuration (FIGS. 7, 9 and 11) ofthe cutting element 104. The cutting element 104 is generally comprisedof a cutting blade portion 130 configured to cut into bone tissue, and ashaft or rod portion 132 configured to operatively coupled the cuttingblade portion 130 to the actuator mechanism 106. In one embodiment ofthe invention, the cutting blade 130 includes a cutting edge 134 havinga profile corresponding to the outer profile of the tapping thread 120.The cutting blade 130 preferably defines a pair of thread-likeprotrusions 136 a, 136 b that correspond in size and shape to adjacentrevolutions of the tapping thread 120. It should be understood, however,that the cutting blade 130 may include any number of protrusions,including a single protrusion or three or more protrusions. It shouldalso be understood that the cutting blade 130 may be configured suchthat the cutting edge 134 has an outer profile that does not correspondto the outer profile of the tapping thread 120. For example, as shown inFIG. 14, a cutting blade 310 may be provided which includes a cuttingedge 312 having an outer profile defining a substantially flat,rectangular configuration. As should be appreciated, other shapes andconfigurations of cutting blades are also contemplated that would besuitable for forming an enlarged cross-sectional portion of a passage inbone tissue. Furthermore, although the cutting element 104 has beenillustrated and described as including a single cutting blade 130, itshould be understood that the cutting element 104 could include anynumber of cutting blades 130 arranged at a single axial location alongthe elongated member 102 or at multiple axial locations along elongatemember 102.

Notably, when the cutting blade 130 is disposed in the retractedconfiguration, the cutting edge 134 is aligned with the outer profile ofadjacent revolutions of the tapping thread 120, but preferably does notextend beyond the outer profile of the tapping thread 120. As will bediscussed in further detail below, when disposed in the retractedconfiguration, the cutting blade 130 will pass through the threadedaxial passage formed in the bone tissue by the tapping thread 120without disrupting or interfering with the formed threads. However, whentransitioned to the expanded configuration, the cutting edge 134 ofcutting blade 130 will extend beyond the outer profile of adjacentrevolutions of the tapping thread 120. As will also be discussed infurther detail below, when disposed in the expanded configuration, thecutting blade 130 will cut into bone tissue to form an enlargedcross-sectional portion of the axial passage.

In a preferred embodiment of the present invention, the cutting blade130 is transitioned between the retracted and expanded configurations byaxially displacing the cutting blade 130 relative to the elongate member102. As shown in FIGS. 10 and 11, the elongate member 102 defines anaxial channel or passageway 150 extending along the distal end portion102 b. The channel 150 includes an axial section 152 having asubstantially flat, non-tapered bottom surface 154 arranged generallyparallel with longitudinal axis L, and a ramped or inclined section 156having an outwardly tapering bottom surface 158 arranged at an acuteangle α relative to longitudinal axis L. In one embodiment of theinvention, the tapered surface 158 has a curvilinear or arcuateconfiguration, with a tangent line T of the curve being arranged at anangle α relative to the longitudinal axis L. The angle α preferablyfalls within a range of 0 degrees to about 45 degrees. However, otherangles α are also contemplated as falling within the scope of thepresent invention, including angles α greater than 45 degrees.Additionally, although the tapered surface 158 has been illustrated anddescribed as having a curvilinear or arcuate configuration, it should beunderstood that surface 158 may alternatively have an angularconfiguration, tapering outwardly at a substantially constant angle α.

The cutting element 104 is sized and shaped to be slidably displacedwithin the axial channel 150. Preferably, the cutting element 104 has awidth w₁ that is slightly less than the width w₂ of the channel 150 toallow the cutting element 104 to be guidably displaced along the axialchannel 150 (See FIG. 9). Additionally, the shaft 132 preferably has aheight h₁ that is slightly less than the height h₂ between the bottomsurface 154 of channel 150 and the root diameter of the tapping thread120. As should be appreciated, the height h₁ of the shaft 132 is sizedto avoid interfering with the tapping operation performed by the tappingthread 120 and to avoid disruption of the threads formed in the bonetissue. Similarly, when disposed in the retracted configuration, thecutting blade 130 defines a cutting profile corresponding to the outerprofile of the tapping thread 120 to avoid interfering with the tappingoperation and to avoid disruption the threads formed in the bone tissue.

As will be discussed below, the cutting blade 130 is preferablytransitioned between the retracted configuration illustrated in FIG. 10and the expanded configuration illustrated in FIG. 11 in response to amechanically induced force. Such force may be effected, for example, viathe selective actuation of the actuator mechanism 106. The cutting blade130 is transitioned from the retracted configuration toward the expandedconfiguration by axially displacing the cutting element 104 along thechannel 150 in the direction of arrow A until a lower bearing surface160 of the cutting blade 130 is engaged against the outwardly taperingsurface 158 of the ramped section 156. As the bearing surface 160 isslidably advanced along the tapered surface 158, the cutting blade 130will correspondingly be urged in an outward or lateral direction towardthe expanded configuration illustrated in FIG. 11. Preferably, thebearing surface 160 is rounded or beveled to avoid cutting into thetapered surface 158 as the cutting blade 130 is displaced along channel150. As should be apparent, the cutting blade 130 may be transitionedback toward the retracted configuration illustrated in FIG. 10 bydisplacing the cutting element 104 along the channel 150 in thedirection of arrow B until the lower bearing surface 160 of the cuttingblade 130 disengages the tapered surface 158 of ramped section 156.Although the illustrated embodiment of the invention depicts channel 150as including the tapered surface 158, it should be understood that thecutting blade 130 could alternatively define a tapered surfaceconfigured to interact with a portion of the elongate member 102 tofacilitate transitioning of the cutting blade 130 between the retractedand expanded configurations.

Referring to FIGS. 12 and 13, shown therein is an actuator mechanism 106according to one embodiment of the present invention. The actuatormechanism 106 is coupled to the cutting element 104 and is operable toselectively transition the cutting blade 130 between the retracted andexpanded configurations. In the illustrated embodiment, the actuatormechanism 106 is configured as a collet or ring engaged about theelongate member 102 and operatively coupled to the shaft 132 of cuttingelement 104. As should be appreciated, axial displacement of the collet106 in the direction of arrow A or arrow B correspondingly displaces thecutting element 104 through the channel 150 and slidably displaces thecutting blade 130 along the ramped section 156 to transition the cuttingblade 130 between the retracted and expanded configurations. A pair ofstop members 170, 172 are preferably attached to the elongate member 102and disposed on either side of the collet 106 to limit axialdisplacement of the collet 106 and corresponding axial displacement ofthe cutting element 104.

In one embodiment of the present invention, the collet 106 has acylindrical configuration, defining an inner surface 180 having adiameter slightly larger than the diameter of an outer surface 182 ofthe elongate member 102. As a result, the collet 106 may be slidably andguidably displaced along the outer surface 180 of the elongate member102. Although the surfaces 180, 182 have been illustrated and describedas having a circular cross section, it should be understood that othercross-sections are also contemplated, such as, for example, square orrectangular cross-sections.

The collet 106 preferably defines a blind keyway 184 generally alignedwith the axial portion 152 of channel 150 and having a widthapproximately equal to the channel width w₂. The shaft 132 of cuttingelement 104 preferably includes a U-shaped portion 186 including a lowerleg 188 a and an upper leg 188 b. The U-shaped portion 186 of shaft 132is positioned within the keyway 184 and is secured to the collet 106 byway of a number of fasteners 190, such as, for example, a pair ofopposing sets of set screws engaging opposite sides of the upper leg 188b. The height of the keyway 184 is preferably sized somewhat less thanthe height of the U-shaped portion 186 such that the U-shaped portion186 is resiliently deformed as it is inserted into the keyway 184. As aresult, an inward biasing force is established to aid in maintaining theblade portion 130 and the shaft portion 132 in their proper positionwithin channel 150. Notably, the inward biasing force maintains thebottom surfaces of the cutting blade 130 and the shaft 132 in constantengagement against the bottom surface of the channel 150.

Although a specific embodiment of an actuator mechanism 106 has beenillustrated and described herein, other embodiments of actuatormechanisms are also contemplated as would occur to one of skill in theart. It should be understood that any type of actuator mechanismconfigured to transition the cutting element 104 between the retractedand expanded configurations may be used. For example, in an alternativeembodiment of the invention, the actuator mechanism 106 may bethreadingly engaged with the elongate member 102 and coupled to thecutting element 104 in such a manner as to axially displace the cuttingelement 104 relative to the elongate member 102 to transition thecutting element between the retracted and expanded configurations. Inone such embodiment, the inner surface 180 of collet 106 may bethreadingly engaged with the outer surface 182 of the elongate member102, with the shaft portion 132 of the cutting element 104 beingrotatably coupled to the collet 106. As should be appreciated, rotationof the collet 106 would correspondingly axially displace the cuttingelement 104 relative to the elongate member 102 to transition thecutting blade 130 between the retracted and expanded configurations.

Having described various structural features of the surgical instrument100, a method of using the surgical instrument 100 to form an axialpassage in bone having an enlarged cross-section portion will now bediscussed in accordance with one form of the present invention.Referring to FIGS. 15 and 16, shown therein is the formation of an axialpassage 400 through the pedicle region P of a vertebral body V and intoan interior region of the vertebral body V. The axial passage 400 has athreaded portion 402 and an enlarged cross-sectional portion 410, thefunction of which will be discussed below.

Referring to FIG. 15, with the cutting blade 130 disposed in theretracted configuration (FIG. 6), the distal end portion 102 b of theelongate member 102 is engaged with the pedicle P of the vertebral bodyV and the elongate member 102 is rotated about the longitudinal axis Lvia application of rotational force to the handle 110. As a result,internal threads 404 having an outer thread diameter d₁ are cut into thebone tissue via the tapping thread 120 to form the threaded portion 402of the axial passage 400 at a predetermined depth. As discussed above,the cutting edge 134 of cutting blade 130 preferably does not extendbeyond the outer profile of the tapping thread 120 when in the retractedconfiguration. As a result, the cutting blade 130 will pass through thethreaded portion 402 of axial passage 400 without interfering with thetapping operation and without disrupting or otherwise damaging theinternal threads 404.

In one embodiment of the invention, a pilot hole 406 is initially formedin the vertebral body V prior to performing the tapping operation.However, it should be understood that in another embodiment of theinvention, the distal end portion 102 b of the elongate member 102 mayinclude a self-drilling feature to eliminate the need for a pilot hole406. As illustrated in FIG. 14, such features may include, for example,the incorporation of a pointed tip and/or a cutting flute into thedistal end potion 102 b to facilitate penetration and cutting into bonetissue.

Referring to FIG. 16, following formation of the threaded portion 402 ofaxial passage 400, the cutting blade 130 is transitioned to the expandedconfiguration (FIG. 7). As discussed above, transitioning between theretracted and expanded configurations is accomplished by axiallydisplacing the cutting blade 130 relative to the elongate member 102,such as might be accomplished, for example, by slidably displacing thecollet 106 along the elongate member 102 in the direction of arrow A.The elongate member 102 is then rotated about the longitudinal axis Lvia application of a rotational force to the handle 110. As a result,the protrusions 136 a, 136 b of the cutting blade 130 will cut into theadjacent bone tissue to form an enlarged cross-sectional portion 410 ofthe axial passage 400. As discussed above, the cutting edge 134 of thecutting blade 130 extends beyond the outer profile of the tapping thread120 when in the expanded configuration to thereby form thread-likegrooves 412 having an outer diameter d₂ somewhat larger than the outerthread diameter d₁ of threads 404.

Following formation of the enlarged cross-sectional portion 410, thecutting blade 130 is transitioned back to the retracted configuration(FIG. 6), such as might be accomplished, for example, by slidablydisplacing the collet 106 along the elongate member 102 in the directionof arrow B. Notably, since the width w₁ of the cutting blade 130 issized in relatively close tolerance with the width w₂ of the axialchannel 150 (FIG. 9), the risk of bone or other debris becoming lodgedbetween the cutting blade 130 and the elongate member 120 issubstantially reduced, if not eliminated entirely. If such a result wereto occur, the cutting blade 130 might be inhibited or restricted fromtransitioning back to the retracted configuration, thereby preventingremoval of the distal portion 102 b of elongate member 102 from theaxial passage 400.

Following transitioning of the cutting blade 130 back to the retractedconfiguration, the distal end portion 102 b of elongate member 102 maythen be removed from the axial passage 400 by unthreading the tappingthread 120 through the threaded portion 402. Since the cutting edge 134of the cutting blade 130 does not extend beyond the outer profile of thetapping thread 120 when in the retracted configuration, the cuttingblade 130 will pass through the threaded portion 402 of axial passage400 without disrupting or otherwise damaging the internal threads 404formed therealong.

Referring to FIGS. 17 and 18, shown therein is one embodiment of a bonescrew 500 suitable for use with the present invention. The bone screw500 is configured to threadingly engage the threaded portion 402 of theaxial passage 400 formed in the vertebral body V. The bone screw 500 isalso configured to deliver an anchoring material into the enlargedcross-sectional portion 410 of the axial passage 400 to secure the bonescrew 500 to vertebral body V and to eliminate or at least minimize thelikelihood of the bone screw 500 from loosening or cutting away fromvertebral body V. In one embodiment of the invention, the anchoringmaterial is bone cement. However, other suitable types of anchoringmaterials are also contemplated as would occur to one of skill in theart.

The bone screw 500 includes a threaded shank portion 502 and a headportion 504. The threaded shank portion 502 defines a screw thread 506corresponding to the threads 404 formed along the threaded portion 402of the axial passage 400. An axial opening 508 extends through the headportion 504 and along a substantial portion of the threaded shank 502.However, the axial opening 508 preferably does not extend entirelythrough the threaded shank 502 so as to define a closed distal end 510.It should be understood, however, that the axial opening 508 couldalternative extend along the entire length of the bone screw 500. Anumber of fenestration openings 512 extend through the bone screw andare disposed in communication with the axial opening 508. Preferably,the fenestration openings 512 are arranged in four axial grouping alongthe threaded shank 502, with the openings 512 in each grouping beinguniformly positioned about the circumference of the threaded shank 502.In one embodiment, each grouping includes three openings 512 uniformlyseparated by 120 degrees. The fenestration openings 512 are preferablydisposed between adjacent revolutions of the screw thread 506 and arepreferably arranged along the distal-half of the threaded shank 502.

The head portion 504 of the bone screw 500 preferably includes a driveportion 520 and a connector portion 522. The drive portion 520 isconfigured to be engaged by a driving tool (not shown) to facilitatethreading insertion of the bone screw 500 in the threaded portion 402 ofaxial passage 400. In one embodiment, the drive portion 520 is enlargedrelative to the connector portion 522 and has a hexagonal shape defininga number of flattened regions 521. However, other configurations of thedrive portion 520 are also contemplated as would occur to one of skillin the art. The connector portion 522 is configured to connect to asystem for delivering anchoring material to the bone screw 500. Theconnector portion 522 is also preferably configured to mate with aconnector member, such as, for example, a rod or plate, and to accept ananchoring device, such as a nut, to secure the rod or plate to the bonescrew 500. In one embodiment, the connector portion 522 comprises athreaded stem extending from the drive portion 520. However, otherconfigurations of the connector portion 522 are also contemplated aswould occur to one of skill in the art.

Although a specific embodiment of a bone screw 500 has been illustratedand described herein, it should be understood that other types andconfigurations of bone screws are also contemplated for use inassociation with the present invention. For example, another embodimentof a bone screw suitable for use in association with the presentinvention is described in U.S. patent application Ser. No. 09/746,668 toChappuis, the contents of which have been incorporated herein byreference. It should also be understood that other types of bone anchorsare also contemplated for use in association with the present invention,including both threaded and unthreaded bone anchor devices.

Referring to FIG. 19, following formation of the axial passage 400within the vertebral body V and removal of the surgical instrument 100therefrom, the bone screw 500 is inserted into the axial passage 400.The bone screw 500 is threaded along the threaded portion 402 of axialpassage 400 until the fenestration openings 512 are disposed adjacentthe enlarged cross-sectional portion 410. Preferably, the threads 506 ofthe bone screw 500 are disposed adjacent and are generally aligned withthe helical grooves 412 of the enlarged cross-sectional portion 410 soas to define a substantially uniform gap or spacing between the threads506 and the adjacent bone tissue. When the bone screw 500 is properlypositioned within the axial passage 400, the head portion 504 ispreferably disposed adjacent the outer surface of the vertebral body V.

Following insertion of the bone screw 500 into the axial passage 400, ananchoring material delivery system is attached to the connector portion522 of head 504. An anchoring material 530, such as, for example, bonecement, is then injected through the axial opening 508, out thefenestration openings 512, and into the enlarged cross-sectional portion410 of the axial passage 400. One example of a system and method forinserting a bone screw into a vertebral body and for delivering ananchoring material thereto is disclosed in U.S. patent application Ser.No. 09/746,668 to Chappuis, the contents of which have been incorporatedherein by reference. However, other suitable systems and methods forinserting a bone screw into a vertebral body and delivering an anchoringmaterial thereto are also contemplated as would occur to one of skill inthe art.

As should be appreciated, the enlarged cross-sectional portion 410 ofthe axial passage 400 facilitates uniform distribution of the bonecement 530 about the threaded shank portion 502 of the bone screw 500while minimizing disruption to the cancellous bone tissue surroundingthe threaded shank 502. Once the bone cement 530 cures or hardens, acement mantle is formed about the threaded shank 502 to firmly securethe bone screw 500 to the vertebral body V. As should also beappreciated, the cement mantle eliminates or at least minimizes thelikelihood of the bone screw 500 from loosening or cutting away from thevertebral body V. As should also be appreciated, formation of theenlarged cross-sectional portion 410 along only a portion of the axialpassage 400, while maintaining the threaded portion 402 at a smaller orreduced cross-section, preserves the structural integrity of thevertebral body V. This is particularly advantageous when the bone screw500 is inserted into the relative delicate pedicle region P of thevertebral body V. In this manner, formation of the axial passage 400 inthe vertebral body V and securement of the bone screw 500 within theaxial passage 400 by way of a cement mantle is accomplished in aminimally invasive manner.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A surgical instrument, comprising: an elongatemember extending along an axis; and at least one cutting element engagedwith said elongate member and being transitionable between a retractedconfiguration for extending through a first portion of a passage in boneand an expanded configuration for forming a second portion of thepassage having an enlarged cross-section; and wherein a portion of saidelongate member defines a tapping thread configured to cut threads alongthe first portion of the passage, and wherein axial displacement of saidat least one cutting element relative to said elongate member causessaid at least one cutting element to transition between said retractedand expanded configurations to form said second portion of the passagehaving said enlarged cross-section.
 2. The instrument of claim 1,wherein said elongate member and said cutting element define bearingsurfaces slidably engaging one another during said axial displacement,at least one of said bearing surfaces including a ramped sectionconfigured to transition said cutting element between said retracted andexpanded configurations during said axial displacement.
 3. Theinstrument of claim 1, wherein said elongate member defines an axialchannel including a ramped section, said at least one cutting elementbeing at least partially disposed within said channel and slidablydisplaced along said ramped section to transition said cutting elementbetween said retracted and expanded configurations.
 4. The instrument ofclaim 3, further comprising an actuator mechanism engaged with saidelongate member and coupled to said at least one cutting element,wherein axial displacement of said actuator mechanism relative to saidelongate member slidably displaces said cutting element along saidramped section of said channel to transition said cutting elementbetween said retracted and expanded configurations.
 5. The instrument ofclaim 4, wherein said actuator mechanism comprises a collet slidablyengaged about said elongate member wherein axial displacement of saidcollet relative to said elongate member slidably displaces said cuttingelement along said ramped section of said channel to transition saidcutting element between said retracted and expanded configurations. 6.The instrument of claim 1, wherein said elongate member comprises asleeve, said at least one cutting element being outwardly biased towardsaid expanded configuration and being at least partially disposed withinsaid sleeve to selectively maintain said at least one cutting element insaid retracted configuration, said at least one cutting element beingtransitionable between said retracted and expanded configurations byaxially displacing said at least one cutting element relative to saidsleeve.
 7. The instrument of claim 6, further comprising an actuatormechanism including a shaft disposed within said sleeve and coupled tosaid cutting element, wherein axial displacement of said shaft relativeto said sleeve transitions said at least one cutting element betweensaid retracted and expanded configurations.
 8. The instrument of claim6, wherein said at least one cutting element is pivotally coupled tosaid shaft and is aligned in an axial orientation when in said retractedconfiguration and in angular orientation when in said expandedconfiguration.
 9. A surgical instrument, comprising: an elongate member;a first cutting element disposed along said elongate member for forminga first portion of a passage in bone, said first cutting elementcomprising a tapping thread; and a second cutting element disposed alongsaid elongate member and being transitionable between a retractedconfiguration for extending through the first portion of the passage andan expanded configuration for forming a second portion of the passagehaving an enlarged cross-section.
 10. The instrument of claim 11,wherein said first cutting element comprises a drill flute.
 11. Theinstrument of claim 11, wherein said first cutting element comprises adistal end portion of said elongate member.
 12. The instrument of claim9, wherein said second cutting element comprises a cutting bladeextending laterally from said elongate member when transitioned towardsaid expanded configuration.
 13. The instrument of claim 12, whereinsaid elongate member defines a channel extending along an axis with saidcutting blade being at least partially disposed within said channel, atleast one of said channel and said cutting blade including a rampedsection configured to transition said cutting blade between saidretracted and expanded configurations when said cutting blade is axiallydisplaced along said channel.
 14. The instrument of claim 13, furthercomprising an actuator mechanism engaged with said elongate member andcoupled to said cutting blade, wherein axial displacement of saidactuator mechanism relative to said elongate member axially displacessaid cutting blade along said channel to transition said cutting bladebetween said retracted and expanded configurations.
 15. A surgicalinstrument, comprising: an elongate member; a first cutting elementdisposed along said elongate member for forming a first portion of apassage in bone, said first cutting element comprising a distal endportion of said elongate member, said distal end portion of saidelongate member configured to be self-drilling and self-tapping; and asecond cutting element disposed along said elongate member and beingtransitionable between a retracted configuration for extending throughthe first portion of the passage and an expanded configuration forforming a second portion of the passage having an enlargedcross-section.
 16. A surgical instrument, comprising: an elongatemember; a first cutting element disposed along said elongate member forforming a first portion of a passage in bone; and a second cuttingelement disposed alone said elongate member and being transitionablebetween a retracted configuration for extending through the firstportion of the passage and an expanded configuration for forming asecond portion of the passage having an enlarged cross-section; andwherein said first cutting element comprises a tapping thread andwherein said second cutting element comprising a cutting blade.
 17. Theinstrument of claim 16, wherein said cutting blade includes a cuttingedge having a profile corresponding to a profile of said tapping thread.18. A surgical instrument, comprising: an elongate member; a tappingthread defined along a portion of said elongate member for forming athreaded portion of a passage in bone; and a cutting blade engaged withsaid elongate member and being transitionable between a retractedconfiguration for extending through the threaded portion of the passageand an expanded configuration for forming an enlarged cross-sectionalportion of the passage.
 19. The instrument of claim 18, wherein saidelongate member defines an axial channel including a ramped section,said cutting blade being at least partially disposed within said channeland slidably displaceable along said ramped section to transition saidcutting blade between said retracted and expanded configurations. 20.The instrument of claim 19, further comprising a collet engaged withsaid comprises a collet slidably engaged about said elongate member andcoupled to said cutting blade so that axial displacement of said colletrelative to said elongate member slidably displaces said cutting bladealong said ramped section of said channel to transition said cuttingblade between said retracted and expanded configurations.
 21. Theinstrument of claim 18, wherein said cutting blade includes a cuttingedge having a profile corresponding to a profile of said tapping thread.22. A surgical instrument, comprising: means for tapping threads along aportion of a passage in bone; means for forming an enlargedcross-sectional portion of the passage; and means for transitioning saidmeans for forming between a retracted configuration for extendingthrough the threaded portion of the passage and an expandedconfiguration for forming the enlarged cross-sectional portion of thepassage.
 23. A surgical instrument, comprising: an elongate memberextending along an axis and including: a tapping portion formed alone adistal portion of said elongate member and configured to cut threadsalong a passage in bone; and an expandable portion having at least onecutting element transitionable between an axial orientation configuredto extend through the axial passage in bone and an angular orientationfor enlarging a portion of the axial passage laterally adjacent saidthreads.
 24. The instrument of claim 23, wherein said at least onecutting element is pivotally coupled to said elongate member.
 25. Theinstrument of claim 24, wherein said at least one cutting element ispivotally coupled to a distal end portion of said elongate member. 26.The instrument of claim 23, wherein said at least one cutting element isoutwardly biased toward said angular orientation and is initiallymaintained in said axial orientation by a retention element.
 27. Theinstrument of claim 26, wherein said retention element is a sleeve, saidat least one cutting element being at least partially disposed withinsaid sleeve to selectively maintain said at least one cutting element insaid axial orientation, said at least one cutting element beingtransitionable between said retracted and expanded configurations byaxially displacing said at least one cutting element relative to saidsleeve.
 28. The instrument of claim 27, further comprising an actuatormechanism including a shaft disposed within said sleeve and coupled tosaid at least one cutting element, wherein axial displacement of saidshaft relative to said sleeve transitions said at least one cuttingelement between said axial and angular configurations.
 29. Theinstrument of claim 28, wherein said at least one cutting element ispivotally coupled to said shaft.
 30. The instrument of claim 23, whereinthe axial passage is formed by applying an axial force to said elongatemember; and wherein the axial passage is enlarged by applying arotational force to said elongate member.
 31. The instrument of claim30, further comprising a handle coupled to said elongate member, saidhandle configured to transmit said axial and rotational forces to saidelongate member.
 32. The instrument of claim 23, further comprising aretention element configured to selectively maintain said at least onecutting element in said axial orientation.
 33. A surgical instrument,comprising: an elongate member extending along an axis; a tappingelement formed along a distal portion of said elongate member; and atleast one cutting element transitionable between a retractedconfiguration for extending through a passage in bone and an expandedconfiguration for enlarging a portion of the passage; and wherein saidtapping element is configured to cut threads along the passage, said atleast one cutting element configured to enlarge said portion of thepassage laterally adjacent said threads when transitioned to saidexpanded configuration.
 34. The instrument of claim 33, wherein said atleast one cutting element has a lateral profile corresponding to alateral profile of said tapping element.
 35. The instrument of claim 33,wherein axial displacement of said at least one cutting element relativeto said elongate member causes said at least one cutting element totransition between said retracted and expanded configurations.
 36. Theinstrument of claim 35, wherein said elongate member and said cuttingelement define bearing surfaces slidably engaging one another duringsaid axial displacement, at least one of said bearing surfaces includinga ramped section configured to transition said cutting element betweensaid retracted and expanded configurations during said axialdisplacement.
 37. The instrument of claim 33, wherein said elongatemember includes another cutting element configured to form the passagein the bone.
 38. The instrument of claim 37, wherein said anothercutting element comprises a portion of said tapping element.